Mihaela Gorgoi 20.05.2009
The BESSY HIKE Project The BESSY HIKE Project
Mihaela Gorgoi
Mihaela Gorgoi 20.05.2009
IR to x-Ray (11 x-Ray Beamlines)29 ID-Beamlines25 DIP-Beamlines
4 lin. Undulators6 ell. Undulators
1.7 GeV 300 mA16 straight sections
3 7T-WLS1 7T-Wiggler
VUVXUV:
x-Ray:
BESSY II
Mihaela Gorgoi 20.05.2009
Photoemission Photoemission SpectroscopySpectroscopy
monochromatic photon beam ionises electrons from sample
the kinetic energy (Ekin ) of photoelectrons in vacuum outside sample is measured
Ekin = hν
- BEbinding energy of electrons in the sample
• core levels strongly localized, thus BE's give elemental identification• chemical shifts give information on: chemical environment of emitter atoms
oxidation / valence / bonding state
Mihaela Gorgoi 20.05.2009
Why high kinetic energy ? Why high kinetic energy ?
Large Sampling Depth
(Bulk sensitive)
Less Surface Sensitive
Non-destructive
Advantages
Disadvantage
Low photoionization cross sections
Bulk structures, multilayers, buried nano layers and interfaces
Typical samples:
10 100 1000 100000,1
1
10
100
0,1
1
10
100
2
Total yieldin transitionmetals and rare earths
"classic" range for photoelectron spectroscopy
HIKE - range
extrapolated:Electron escape depths - experimental:
Inel
astic
mea
n fr
ee p
ath
(nm
)
Electron kinetic energy (eV)
Mihaela Gorgoi 20.05.2009
KMCKMC--1 Beamline 1 Beamline Double-crystal monochromator:
angular range 5° - 82°Si (111) 1997 - 12000 eVSi (422) 5639 - 12000 eVSi (311) 4000 - 12000 eV
F. Schäfers, M. Mertin, M. Gorgoi, Rev. Sci. Instrum. 78 (2007) 123102
toroidalmirror
11540 11800
6 mrad
apertureBe-foil
12978 28098 35273distance to source (mm)
top view
aperture wall focus
0
InSbSi 111Si 311Si 422
distance between elements (mm)15120 717512978
3 mrad
source
179.2 °
328
side view
crystal 1
crystal 2
<0.5 mrad
<0.2 mrad
Mihaela Gorgoi 20.05.2009
2 4 6 8 10
0.1
1
10
Si (444)Si (333)
InSb (111)
Si (111)
Si (311)
Si (422)
Res
olut
ion
(eV
)
Energy (keV)2 4 6 8 10 12 14
108
109
1010
1011
1012
Energy (keV)
Si (422)
In LIII,II,I
Pt LIII
Sb LIII,II,I
Pt LII
Phot
on F
lux
/ 100
mA
InSb (111)
Si (111)
Pt LI
The resolution becomes very high at certain photon energies
KMCKMC--1 Beamline 1 Beamline
Mihaela Gorgoi 20.05.2009
The HIKE SetThe HIKE Set--upupMotorized
5-axis samplemanipulator:
Electronspectrometer:Scienta R4000 optimized for high kinetic
energies up to 10 KeV
Load-lockfor sample
introduction & storage
Motorized chamber
stand
KMC-1
M. Gorgoi et al. Nucl. Instrum. and Meth. A 601 (2009) 48
Mihaela Gorgoi 20.05.2009
Typical Experiment Typical Experiment
FermiFermi levellevel of Au(111)of Au(111)
Inte
nsity
[arb
itrar
y un
its]
2006.02005.62005.22004.8Kinetic Energy [eV]
0.27 eV width @ RT
Excitation energy:2010 eV
Gaussian contribution = Gaussian contribution = beamline resolution:beamline resolution:~ ~ 0.22 0.22 eVeV
M. Gorgoi et al. Eur. Phys. J. Special Topics 169, 221–225 (2009)
AnalyzerAnalyzer::PE 200 / 0.3 mm PE 200 / 0.3 mm slitslit150 150 meVmeV
resolutionresolution
TheThe
HIKE HIKE station at BESSY IIstation at BESSY II
Chamber stand positioning
accuracy within 2 μm !
Mihaela Gorgoi 20.05.2009
HIKE on Au: Depth Profiling with HIKE on Au: Depth Profiling with Fixed Monochromator SettingFixed Monochromator Setting
Si (444)Si (444)2 hours2 hours
Si (111)Si (111)4 min.4 min.
ΔΔE=E=0.210.21±±0.01 0.01 eVeV
Si (333)Si (333)40 min.40 min.
ΔΔE=E=0.0500.050±±0.02 0.02 eVeV ΔΔE=E=0.0730.073±±0.02 0.02 eVeV
Inte
nsity
(arb
. un.
)
19161914191219101908Kinetic Energy / eV
Au 4f Si(111)2002 eV
Inte
nsity
(arb
. un.
)
59205918591659145912Kinetic Energy / eV
Si(333)6006 eV
Au 4f
Inte
nsity
(arb
. un.
)
79227920791879167914Kinetic Energy / eV
Au 4f Si(444)8008 eV
F. Schäfers, M. Mertin, M. Gorgoi, BESSY Annual Report 2006, 211
Mihaela Gorgoi 20.05.2009
Selected ResultsSelected Results
•• Metal multilayers Metal multilayers –– interdiffusioninterdiffusion
•• OrganicOrganic and inorganic solarand inorganic solar cellscells
•• XX--ray standing wavesray standing waves
•• Ni 1s and satellitesNi 1s and satellites
Mihaela Gorgoi 20.05.2009
Addressing interfacial quality in Addressing interfacial quality in CuNi multilayersCuNi multilayers
Grown by UHV-based dc magnetron sputtering
Bilayers: 5ML Cu / 5ML Ni5ML Cu / 5ML Ni
Heating to a preset temperature2010 eV excitation energy 0.26 eV overall resolution
E. Holmström, W. Olovsson, I.A. Abrikosov, A.M.N. Niklasson, B. Johansson, M. Gorgoi, O. Karis, S. Svensson, F. Schäfers, W. Braun, G. Öhrwall, G. Andersson, M. Marcellini, W. Eberhardt, Phys. Rev. Let. 97
(2006)
266106
Mihaela Gorgoi 20.05.2009
Imperfect interfacesImperfect interfaces
✦
What we observe as ”one”
core photoelectron line is in reality an envelope originating from a distribution of many chemically shifted core levels.
✦
A calculation of the chemical shift therefore originates from many calculations (using DFT and other tricks)
Use a GAUSSIAN distribution of chemically inequivalent atoms around the interface, where the imperfection is described by the distribution width Γ
Mihaela Gorgoi 20.05.2009
Example: Example: x
= 5 ML
Interface Interface TheoreticalTheoretical
ModelModel
••
ΓΓ
describes the quality of the describes the quality of the interfaceinterface
Ni NiCu
Results SummaryResults Summary
E. Holmström, W. Olovsson, I.A. Abrikosov, A.M.N. Niklasson, B. Johansson, M. Gorgoi, O. Karis, S. Svensson, F. Schäfers, W. Braun, G. Öhrwall, G. Andersson, M. Marcellini, W. Eberhardt, Phys. Rev. Let. 97
(2006)
266106
the experimentally determined shifts converge towards the theoretically predicted value of dilute alloy state.
Mihaela Gorgoi 20.05.2009
Results: Cu 2p3/2 spectra of NiResults: Cu 2p3/2 spectra of Ni55CuCu55
2nd experiment –
new samples with the same composition
Mihaela Gorgoi 20.05.2009
Results: Binding energies ofResults: Binding energies of 22--peakpeak--fit components in Nifit components in Ni55CuCu55
Mihaela Gorgoi 20.05.2009
The intensities of Cu 2p, Ni 2p core-levels relative to the intensity of Pt 4f core level from the cap.
Intensity variations in surveysIntensity variations in surveys
Mihaela Gorgoi 20.05.2009
Repeated heating results in alloying of the cap into the
multilayer!
Mihaela Gorgoi 20.05.2009
Cu 2p3/2 coreCu 2p3/2 core--level spectra of level spectra of NiNi55CuCu55
wwithout Pt capithout Pt cap
Mihaela Gorgoi 20.05.2009
Cu 2pCu 2p3/23/2
corecore--level spectra of level spectra of NiNi55CuCu55
without Pt capwithout Pt cap
Similar to previous data for low -
intermediate
temperature anneal
Core level shift almost vanish for high temperatures?!
Mihaela Gorgoi 20.05.2009
Cu enrichment of surface during repeated anneals at high temperatures
Intensity ratiosIntensity ratios
of Niof Ni55CuCu55 without Pt capwithout Pt cap
Mihaela Gorgoi 20.05.2009
We recover the picture from the first published results.
At 6 keV
excitation energy the contribution from the outermost layers is further suppressed.
Cu 2pCu 2p3/23/2
corecore--level spectra of level spectra of NiNi55CuCu55
without Pt cap without Pt cap --
6 6 keVkeV
Mihaela Gorgoi 20.05.2009
HIKE on HIKE on OrganicOrganic ThinThin Film Solar Film Solar CellsCells
F8DTBT PCBM
Sample: polymer blend (1:1)
• At 2keV none of the shake-up features characteristic to the C60 cage are present. no surface presence of PCBM.
• The presence of the shake-ups at 6keV indicates the segregation of PCBM to the inner layers of the film.
M.P.Felicissimo, D.M.Jarzab, M.Gorgoi, M.A.Loi, M.Foster, U.Scherf, M.Scharber, S.Mattila, P.Rudolf, S. Svensson, BESSY annual
report
2007, 241 & J. Mat. Chem. accepted
C60 cage
PCBMF8DTBT+PCBM F8DTBT+PCBM
Mihaela Gorgoi 20.05.2009
MetalMetal--LigandLigand
Interaction in the Valence Interaction in the Valence Electronic Structure of Ruthenium ComplexesElectronic Structure of Ruthenium Complexes
Binding Energy [eV]
4
3
2
0
14 12 10 8 6 4 2
CN2 Cl2 N719 BD
Inte
nsity
[a.u
.]
NN
NN
Ru NCS
NCSCOOH
COO TBA
COOH
COO TBA
- +
- +
Dye 2 (N719)
NN
RuN
NCS
NCS
NCS
Dye 1 (BD)
-+
COOH
COO
-+COO
TBA +
TBA
TBA
NN
NN
Ru CN
CNCOOH
COOH
COOH
COOH
Dye 3(CN2)
NN
NN
Ru Cl
ClCOOH
COOH
COOH
COOH
Dye 4 (Cl2)
• HOMO is determined as a function of ligands•
The splitting of the Ru 4d level into two peaks
depends on the ligands.
E.M.J. Johansson, M. Odelius, M. Gorgoi, O. Karis, R. Ovsyannikov, F. Schäfers, S. Svensson, H. Siegbahn, H. Rensmo, Chem. Phys. Let. 464 (2008) 192
Mihaela Gorgoi 20.05.2009
HIKE on HIKE on InorganicInorganic
ThinThin
Film Solar Film Solar CellsCells
Cu(In,Ga)Se2 (CIGS)Zn(O,S) -
15 nm buffer
layer
Glass + Mo
Inte
nsity
/ a.
u.
2500eV 2000 1500 1000Binding Energy / eV
Se2p
Ga2p
Cu2p
9000eV 8000eV 7000eV 6500eV 6000eV 5500eV 5000eV 4000eV 3000eV
Inte
nsity
/ a.
u.
1500eV 1480 1460 1440 1420Binding Energy / eV
Se2p
Inte
nsity
/ a.
u.
960eV940920Binding Energy / eV
Cu2p
Above approximately 5 keV excitation energy the absorber becomes visible!
Depth profiling of Depth profiling of the devicethe device is is
possible!possible!
E.M.J. Johansson et al, BESSY annual
report
2006, 508 F. Schäfers,
M. Mertin, M. Gorgoi,
Rev. Sci. Intrum. 78 123102 (2007)
S 1s
Zn 2s 2p
Se 2p
Cu 2p
Se 2p
Ga 2p
Cu 2p
Mihaela Gorgoi 20.05.2009
Cu-Diffusion into In2 S3 -Cover Layer
Cu 2p3/2
Cu(In,Ga)Se2
20 nm In2 S3Excitation energy: 4000 eVHeating rate: 2˚
C/min
Kinetic Energy [eV]Temperature [°C]
Countrate[kcts/s]
P.Pistor, N.Allsop, W.Braun, R.Caballero, C.Camus, Ch-H.Fischer, M.Gorgoi, A.Grimm, B.Johnson, T.Kropp, I.Lauermann, S.Lehmann, H.Mönig, S.Schorr, A.Weber, R.Klenk, Physica Status Solidi A 206 (2009) 1059
Mihaela Gorgoi 20.05.2009
X-ray Standing Waves
Standing wave formation in reflection from a surface,Standing wave formation in reflection from a surface,or singleor single--crystal Bragg planes, or a multilayer mirrorcrystal Bragg planes, or a multilayer mirror
Incident Reflected
Standing waves via Bragg reflection of hard x-rays. B.W. Batterman, Phys. Rev A 133, 759 (1964)
ee--hν
RI
courtesy Chuck Fadley
Mihaela Gorgoi 20.05.2009
X-ray Standing Waves - SWEDGE
Scanned sampleSi-wafer
WSiO2
W
Cr wedge
B4C
Fe
B4CMultilayer
Mirror
∼6.0 mm
Scanned standing wave
MFe
dML
1st order Bragg:λx =2dML sinθBragg
λSW (|E2|) =λx /2sinθinc
≈
dML
BuriedInterface
X-ray
Photo-Electron
Or SoftX-ray
∼0.1 mmspot
θBragg
Fixed phase
Probing Buried Interfaces:
The Standing Wave- Wedge Method
courtesy Chuck Fadley
Mihaela Gorgoi 20.05.2009
Al 1s
O 1sAlOx
O 1sMgO Mg 1s
Fe 2p
20 m
m
80 x 39.8 Å
Si/Mobilayers
SiO
2
Fe-0
-200
ÅM
gO-2
0 Å
AlO
x-2
0 Å
Dee
per
39.8 Å
F. Schonbohm, U.Berges, S.Döring, M. Gorgoi,C. Westphal, D. Buergler, C. Schneider, C. Papp, B. Balke, C.Fadley...
Mo
Si
Mihaela Gorgoi 20.05.2009 O. Karis, S. Svensson, J. Rusz, P. M. Oppeneer, M. Gorgoi, F. Schäfers, W. Braun, W. Eberhardt, N. Martensson, Phys. Rev. B 78, 233105 (2008)
HIKE on Ni Core Levels (6 eV satellite)
• DFT calculation: 3d shake up • Difference in core hole screening
and localisation of 1s and 2p states
• Famous, „classical“
problem
in condensed-matter
physics: • Enormous
attention
for
several
decades
-
many
publications
(sampling
surface
or
bulk?)• Correlation
effects
giving
rise
to the
satellites
in the
Ni PES: surface
plasmon
vs. excitonic
states
• Satellites are located at different energyw.r.t. the main 1s (2p) core level line
• Ni 1s measured for the first time !
6 keV
Ni 2p
12.6 keV
Ni 1s
Mihaela Gorgoi 20.05.2009
Summary Summary
0
10
20
30
HIKE Users 2004 - 2009 and beyond
Prop
osal
s
2004 2006 2008 20100
10
20
30
21
20
max.
Jan-June
30
2
9
14
114
14
24
Year
KM
C-1
Bea
mtim
e w
eeks
06.10.2008 FS
Bending magnet Bending magnet beamlinesbeamlines atatthird generation facilities providethird generation facilities provideattractive opportunities for HIKEattractive opportunities for HIKE
‘‘highhigh’’ flux flux continuumcontinuum from soft tofrom soft tohard (2hard (2--12 12 keVkeV))
sometimes sometimes crystal limited resolutioncrystal limited resolution(~100 (~100 meVmeV))
resolution always < 1 resolution always < 1 eVeV
HIKE allows depth profiling of realdevices, especially electronicproperties of buried interfaces
HIKE allows determination of corelevel energy shifts
Mihaela Gorgoi 20.05.2009
Acknowledgements
HZB, BESSY II, Berlin:
Franz SchäfersMarcel MertinWalter Braun Wolfgang Eberhardt
Uppsala Universitet:
Svante SvenssonHans SieghbanHakan RensmoErik Johannson
University of Groningen:
Marcella P. FelicissimoPetra Rudolf
IFW, BESSYJörg Fink
TIFRKalo Maiti
University of AmsterdamMark GoldenSanne de Jong
WMIAndreas Erb
Sari GranrothOlof KarisRonny Knut
MPI-FKS'Abt. Keimer'
University of Dortmund:
Sven DöringFrank SchonbohmUlf BergesCarsten Westphal
University of California
Chris Papp, Benny BalkeChuck Fadley